A method for preparing a profiled thin-walled porous material gas-tight coating

Abstract

This invention discloses a method for preparing an airtight coating of a non-porous, thin-walled material, belonging to the technical field of ceramics. The method includes the following steps: pretreatment of the porous material, deposition of a silica-based thin layer, and sealing with an organosilicon-TEOS hybrid system. This invention solves the problems of weak interfacial bonding and poor airtight durability in traditional coatings by constructing a double covalent bond structure. The prepared coating maintains excellent airtight performance even after temperature changes and vibration. The airtight coating prepared by this method exhibits a pressure drop of less than 0.01 MPa over 60 minutes in direct negative pressure testing, negative pressure testing after temperature change cycling, and negative pressure testing after vibration testing, meeting the long-term airtightness requirements under complex service environments.

Description

Technical Field

[0001] This invention belongs to the technical field of ceramics, specifically relating to a method for preparing an airtight coating for a non-circular, thin-walled, porous material. Background Technology

[0002] Irregularly shaped thin-walled porous materials are mostly made of ceramics. Due to their excellent wave transmission performance, low density, and high structural adaptability, they are widely used in high-end fields such as aerospace, electronic information, and precision instruments. During service, these materials often need to achieve hermetically sealed operation under complex environments (such as frequent temperature changes and vibration shocks). Therefore, the preparation of hermetically sealed coatings is a core technology to ensure their functional reliability. The coatings must not only achieve tight sealing across the entire pore domain but also form a strong bond with the irregularly shaped thin-walled substrate. At the same time, they must have excellent resistance to temperature changes and vibration, and the preparation process must avoid causing thermal stress damage to the thin-walled structure.

[0003] Currently, a common process for airtightening porous materials involves vacuum impregnation with organic resins, particularly weather-resistant silicone resins. This method utilizes the resin's low viscosity to penetrate and fill pores, achieving physical sealing after curing. However, when this process is applied to complex components with irregular shapes, thin walls, and porous structures, its long-term airtight reliability under harsh service environments faces challenges.

[0004] The organic resin and the inert ceramic matrix are primarily bonded by physical adsorption and weak van der Waals forces, with weak chemical bonding. When the component undergoes drastic temperature changes or mechanical vibrations, shear stress is generated at the interface due to the significant difference in thermal expansion coefficients and elastic modulus between the resin and ceramic. This stress can easily lead to the coating peeling off from the substrate, creating potential gas leakage channels and affecting long-term airtightness.

[0005] For irregularly shaped parts with a wide pore size distribution and complex structure, a single organic resin is insufficient to perfectly fill all pores. High-viscosity resin cannot penetrate micropores, while low-viscosity resin may leak from large pores before curing, leading to localized incomplete sealing. Even with multiple impregnation cycles, it is difficult to form a continuous, uniform, and defect-free seal throughout the pores.

[0006] The density of the sealing layer formed after the organic resin has cured is limited by the molecular structure and cross-linking density of the resin itself. Under high pressure differentials or long-term osmotic pressure, gas may slowly leak through the intermolecular gaps within the resin. Furthermore, the resin coating has limited strength and toughness, making it prone to fatigue microcracks under thermal cycling or vibration loads, directly compromising the integrity of the gas seal.

[0007] In summary, traditional organic resin impregnation processes still have certain limitations in terms of interfacial bonding strength, uniform filling of complex pores, intrinsic density of coatings, and long-term environmental stability when dealing with the need for airtight coatings for irregularly shaped thin-walled porous ceramics. These limitations make it difficult to fully meet the long-term and reliable sealing requirements of high-end equipment in complex dynamic environments. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a method for preparing an airtight coating for irregularly shaped thin-walled porous materials, which improves the interfacial bonding force of the airtight coating of irregularly shaped thin-walled porous ceramics, enhances the coating density, and exhibits excellent temperature resistance and vibration resistance.

[0009] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing an airtight coating of a non-porous thin-walled material includes the following steps: pretreatment of the porous material, deposition of a silica-based thin layer, and sealing with an organosilicon-TEOS hybrid system.

[0011] The method for pretreating the porous material is as follows: immerse the porous material in a sodium hydroxide solution and keep it in a constant temperature water bath at 45-55℃ for 18-22 minutes. After taking it out, wash it with deionized water 3-4 times, and then dry it at 65-75℃ for 10-14 hours to obtain the activated porous material.

[0012] The porous material has a pore size of 5-30 μm, an overall wall thickness of 2.5-3 mm, and a porosity of 20-25%; wherein the pores are interconnected structures that penetrate the wall material.

[0013] The porous material is made of quartz ceramic;

[0014] The concentration of the sodium hydroxide solution is 40-60 g / L.

[0015] The method for depositing a silica-based thin layer is as follows: the activated porous material is suspended in a silica-based sol, ensuring that the liquid surface covers the material. Under vacuum conditions, low-frequency ultrasound is applied simultaneously, and the material is immersed for 15-20 minutes. The component is then removed, tilted to drain for 4-6 minutes, and the surface residual droplets are blown away. The material is then placed at room temperature for 2-3 hours to drain most of the free water. Subsequently, the temperature is raised to 35-45℃ and held for 2-3 hours to slowly drain the equilibrium water and reduce volume shrinkage stress. Then, the temperature is raised to 55-65℃ and held for 2-3 hours, and then raised to 70-80℃ and held for 2-3 hours to promote complete hydrolysis and condensation of the sol, forming a dense silica-based thin layer, thus obtaining a silica-based porous material.

[0016] A vacuum environment can expel air bubbles from pores, and the ultrasonic cavitation effect can promote the uniform diffusion of sol in micropores, avoiding incomplete plating or local accumulation.

[0017] The gauge pressure of the vacuum is -0.095 to -0.085 MPa;

[0018] The frequency of the low-frequency ultrasound is 20-40kHz;

[0019] The angle of inclination for draining is 30°-60°;

[0020] The purging pressure is 0.08-0.12 MPa.

[0021] The silica-based sol is prepared by using anhydrous ethanol as a solvent, mixing tetraethyl orthosilicate, anhydrous ethanol and deionized water evenly, adjusting the pH to 2-3 with hydrochloric acid solution, then adding polyvinyl alcohol, and continuing to stir for 65-75 minutes to form a uniform and stable silica-based sol.

[0022] The molar ratio of tetraethyl orthosilicate to anhydrous ethanol is 1:3.6-4.4;

[0023] The amount of deionized water added is based on controlling the viscosity of the silica-based sol at 50-70 mPa·s to meet the requirements of pore wetting.

[0024] The amount of polyvinyl alcohol added is 3%-5% of the total mass of the sol;

[0025] The concentration of the hydrochloric acid solution is 0.4-0.6 mol / L.

[0026] The method for sealing the organosilicon-TEOS hybrid system is as follows: add tetraethyl orthosilicate to organosilicon resin, mix, then add deionized water, stir evenly, add hydrochloric acid solution to adjust the pH to 2-3, then add dibutyltin dilaurate as a condensation catalyst, stir at room temperature for 55-65 minutes to form the organosilicon-TEOS hybrid system.

[0027] The silica-based porous material is immersed in an organosilicon-TEOS hybrid system, with the liquid level 1-2 cm above the component. Under vacuum conditions, low-frequency ultrasound is applied simultaneously, and the immersion time is 50-70 minutes. The component is then removed, the surface resin is wiped clean, and the material is dried at room temperature for 2-3 hours. The temperature is then raised to 30-40℃ and dried for another 2-3 hours. Finally, the temperature is raised to 55-65℃ and cured for 3-4 hours. After cooling, the material is removed and the excess coating on the surface is removed by polishing, resulting in a porous material with an airtight coating.

[0028] The viscosity of the hybrid system is higher than that of silica sol. Extending the impregnation time can ensure that the system penetrates into the micropores and achieves full pore domain sealing.

[0029] The silicone resin is composed of a mixture of high molecular weight silicone resin and low molecular weight silicone resin, with a mass ratio of high molecular weight silicone resin to low molecular weight silicone resin of 10:0.45-0.55.

[0030] The high molecular weight organosilicon resin has a number average molecular weight of 10,000-15,000 g / mol, and the low molecular weight organosilicon resin has a number average molecular weight of 1,000-2,000 g / mol.

[0031] The solid content of the organosilicon resin is 45-55%;

[0032] The gauge pressure of the vacuum is -0.095 to -0.085 MPa;

[0033] The frequency of the low-frequency ultrasound is 20-40kHz;

[0034] The mass ratio of the organosilicon resin, tetraethyl orthosilicate, deionized water, and dibutyltin dilaurate is 100:8-10:3.7-4.3:0.3-0.5.

[0035] The concentration of the hydrochloric acid solution is 0.8-1.2 mol / L.

[0036] Room temperature drying can slowly remove solvent and some free water, avoiding coating cracking caused by capillary force; low temperature pre-curing at 30-40℃ can initiate the hydrolysis reaction of tetraethyl orthosilicate to generate silanol groups, while the organosilicon resin begins to crosslink initially; medium temperature synergistic curing at 55-65℃ causes the silanol groups to undergo a condensation reaction with the silanol groups of the organosilicon resin and the hydroxyl groups on the ceramic surface, generating silicon dioxide in situ and forming an organic-inorganic hybrid sealing layer.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] 1. In the deposition of a silica-based thin layer, the active silanol groups in the sol form Si-O-Si covalent bonds with the hydroxyl groups on the surface of the pretreated substrate. The silanol groups remaining on the surface of the thin layer can then form Si-O-Si covalent bonds again with the silanol / alkoxy groups in the organosilicon-TEOS hybrid system, constructing a dual covalent bond structure of "substrate-silica-based thin layer-organosilicon hybrid layer". This chemical bonding replaces traditional physical adsorption, improves interfacial adhesion, blocks interfacial gas permeation channels, and strengthens the mechanical linkage between the coating and the substrate, thus preventing coating peeling and detachment from the source.

[0039] 2. In the organosilicon-TEOS hybrid system, tetraethyl orthosilicate first undergoes hydrolysis under the synergistic effect of hydrochloric acid catalysis and dibutyltin dilaurate condensation catalysis, generating a large number of active silanol groups (Si-OH). These silanol groups can undergo condensation reactions with silanol groups (Si-OH) or alkoxy groups (Si-OR) on the organosilicon resin molecular chain to form strong Si-O-Si covalent bonds. At the same time, they can also crosslink with Si-OH remaining on the surface of ceramic substrate and silica-based thin layer, ultimately forming stable Si-O-Si covalent bonds between organosilicon resin and inorganic silica.

[0040] The strong bonding between the substrate and the silicone resin interface, along with the enhanced cross-linked network structure of the silicone-TEOS hybrid system, endows the coating with excellent mechanical integrity. Under alternating loads such as vibration, the strong interface ensures efficient stress transfer between the substrate and the coating, avoiding stress concentration and failure origin caused by local debonding. Simultaneously, the internal interpenetrating network dissipates energy. The flexible organic phase absorbs and disperses vibrational energy through molecular chain segment movement, while the rigid inorganic connections provide support and suppress excessive deformation. Together, they significantly delay the initiation and propagation of fatigue cracks and alleviate interfacial shear stress caused by the mismatch in thermal expansion coefficients between the coating and the substrate, thus ensuring that the coating maintains structural integrity and tight sealing even under continuous dynamic loads.

[0041] The Si-O-Si covalent bonds introduced into the silicone resin act as rigid crosslinking points and are uniformly dispersed in the silicone crosslinking network. This can significantly reduce the thermodynamic mismatch between the coating and the substrate and prevent the coating from cracking due to shear stress at the interface during temperature change cycles.

[0042] 3. This invention employs a mixed system of high-molecular-weight and low-molecular-weight silicone resins to achieve gradient and precise filling of the pores in porous materials. The high-molecular-weight silicone resin preferentially fills the larger pores inside the material, forming a basic support framework; while the low-molecular-weight silicone resin can penetrate deeply into the micropores and pore edges not covered by the high-molecular-weight resin, avoiding the defects of traditional single resins such as "large pore leakage and micropore impermeability," achieving complete sealing of the entire pore domain. Combined with an impregnation sealing process, a continuous, uniform, and defect-free airtight coating can be formed on the surface and internal pores of the porous material, ultimately endowing the material with stable and reliable airtight performance.

[0043] 4. The airtight coating prepared by the method of the present invention exhibits a pressure drop of less than 0.01 MPa over 60 minutes in direct negative pressure test, negative pressure test after temperature change cycle, and negative pressure test after vibration test, which can meet the long-term airtightness requirements under complex service environments. Detailed Implementation

[0044] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0045] Example 1

[0046] A method for preparing an airtight coating for an irregularly shaped thin-walled porous material is as follows:

[0047] (1) Pretreatment of porous materials

[0048] The porous material was immersed in a 40 g / L sodium hydroxide solution and kept in a constant temperature water bath at 45 °C for 22 min. After being removed, it was washed three times with deionized water and then dried at 65 °C for 14 h to obtain the activated porous material.

[0049] The porous material is made of quartz ceramic with a pore size of 5-30μm, an overall wall thickness of 2.5mm, and a porosity of 20%; the pores are interconnected structures that penetrate the wall material.

[0050] (2) Deposition of silica-based thin film

[0051] The activated porous material was suspended in a silica-based sol, ensuring that the liquid level covered the material. The vacuum was drawn to -0.085 MPa, and low-frequency ultrasound of 20 kHz was applied simultaneously. The material was immersed for 20 min, removed, tilted at 30° to drain for 6 min, and then blown off the residual droplets on the surface under a pressure of 0.08 MPa. The material was then placed at room temperature for 2 h to remove most of the free water. The temperature was then raised to 35°C and held for 3 h to slowly remove the equilibrium water and reduce the volume shrinkage stress. The temperature was then raised to 55°C and held for 3 h, and then raised to 70°C and held for 3 h to promote the complete hydrolysis and condensation of the sol, forming a dense silica-based thin layer, thus obtaining a silica-based porous material.

[0052] The silica-based sol was prepared by using anhydrous ethanol as a solvent, mixing tetraethyl orthosilicate, anhydrous ethanol and deionized water evenly, adjusting the pH to 2 with 0.6 mol / L hydrochloric acid solution, then adding polyvinyl alcohol, and continuing to stir for 65 min to form a uniform and stable silica-based sol.

[0053] The molar ratio of tetraethyl orthosilicate to anhydrous ethanol is 1:3.6;

[0054] The amount of deionized water added is based on controlling the viscosity of the silica-based sol to 50 mPa·s;

[0055] The amount of polyvinyl alcohol added is 3% of the total mass of the sol.

[0056] (3) Sealing of organosilicon-TEOS hybrid system

[0057] Tetraethyl orthosilicate was added to the organosilicon resin, mixed, and then deionized water was added. The mixture was stirred until homogeneous, and 1.2 mol / L hydrochloric acid solution was added dropwise to adjust the pH to 2. Then, dibutyltin dilaurate was added as a condensation catalyst, and the mixture was stirred at room temperature for 55 min to form an organosilicon-TEOS hybrid system.

[0058] The silica-based porous material was immersed in an organosilicon-TEOS hybrid system, with the liquid level 1 cm above the component. The vacuum was drawn to -0.085 MPa, and low-frequency ultrasound of 20 kHz was applied simultaneously. The immersion was carried out for 70 min. The component was then removed, the surface resin was wiped clean, and the material was dried at room temperature for 3 h. The temperature was then raised to 30 °C and dried for 3 h. Finally, the temperature was raised to 55 °C and cured for 4 h. After cooling, the material was removed and the excess coating on the surface was removed by polishing to obtain a porous material with an airtight coating.

[0059] The silicone resin is composed of a mixture of high molecular weight silicone resin and low molecular weight silicone resin, with a mass ratio of 10:0.45.

[0060] The high molecular weight organosilicon resin has a number average molecular weight of 10,000 g / mol, and the low molecular weight organosilicon resin has a number average molecular weight of 1,000 g / mol.

[0061] The solid content of the silicone resin is 45%;

[0062] The mass ratio of the organosilicon resin, tetraethyl orthosilicate, deionized water and dibutyltin dilaurate is 100:8:3.7:0.3.

[0063] Example 2

[0064] A method for preparing an airtight coating for an irregularly shaped thin-walled porous material is as follows:

[0065] (1) Pretreatment of porous materials

[0066] The porous material was immersed in a 50 g / L sodium hydroxide solution and kept in a constant temperature water bath at 50 °C for 20 min. After being removed, it was washed three times with deionized water and then dried at 70 °C for 12 h to obtain the activated porous material.

[0067] The porous material is made of quartz ceramic with a pore size of 5-30μm, an overall wall thickness of 2.8mm, and a porosity of 22%; the pores are interconnected structures that penetrate the wall material.

[0068] (2) Deposition of silica-based thin film

[0069] The activated porous material was suspended in a silica-based sol, ensuring that the liquid level covered the material. A vacuum was drawn to -0.090 MPa, and low-frequency ultrasound of 30 kHz was applied simultaneously. The material was immersed for 18 minutes, then removed and tilted at 45° to drain for 5 minutes. The surface residual droplets were then blown away under a pressure of 0.10 MPa. The material was then placed at room temperature for 2.5 hours to remove most of the free water. Subsequently, the temperature was raised to 40°C and held for 2.5 hours to slowly remove the equilibrium water and reduce volume shrinkage stress. The temperature was then raised to 60°C and held for 2.5 hours, and then raised to 75°C and held for 2.5 hours to promote complete hydrolysis and condensation of the sol, forming a dense silica-based thin layer, thus obtaining a silica-based porous material.

[0070] The silica-based sol was prepared by using anhydrous ethanol as a solvent, mixing tetraethyl orthosilicate, anhydrous ethanol and deionized water evenly, adjusting the pH to 2.5 with 0.5 mol / L hydrochloric acid solution, then adding polyvinyl alcohol, and continuing to stir for 70 min to form a uniform and stable silica-based sol.

[0071] The molar ratio of tetraethyl orthosilicate to anhydrous ethanol is 1:4;

[0072] The amount of deionized water added is based on controlling the viscosity of the silica-based sol to 60 mPa·s;

[0073] The amount of polyvinyl alcohol added is 4% of the total mass of the sol.

[0074] (3) Sealing of organosilicon-TEOS hybrid system

[0075] Tetraethyl orthosilicate was added to the organosilicon resin, mixed, and then deionized water was added. The mixture was stirred until homogeneous, and 1 mol / L hydrochloric acid solution was added dropwise to adjust the pH to 2.5. Then, dibutyltin dilaurate was added as a condensation catalyst, and the mixture was stirred at room temperature for 60 min to form an organosilicon-TEOS hybrid system.

[0076] The silica-based porous material was immersed in an organosilicon-TEOS hybrid system, with the liquid level 1.5 cm above the component. The vacuum was drawn to -0.090 MPa, and low-frequency ultrasound of 30 kHz was applied simultaneously. The immersion time was 60 min. The component was then removed, the surface resin was wiped clean, and the material was dried at room temperature for 2.5 h. The temperature was then raised to 35 °C and dried for another 2.5 h. Finally, the temperature was raised to 60 °C and cured for 3.5 h. After cooling and removal, the excess coating on the surface was removed by polishing to obtain a porous material with an airtight coating.

[0077] The silicone resin is composed of a mixture of high molecular weight silicone resin and low molecular weight silicone resin, with a mass ratio of 10:0.5.

[0078] The high molecular weight organosilicon resin has a number average molecular weight of 12000 g / mol, and the low molecular weight organosilicon resin has a number average molecular weight of 1500 g / mol.

[0079] The solid content of the silicone resin is 50%.

[0080] The mass ratio of the organosilicon resin, tetraethyl orthosilicate, deionized water and dibutyltin dilaurate is 100:9:4:0.4.

[0081] Example 3

[0082] A method for preparing an airtight coating for an irregularly shaped thin-walled porous material is as follows:

[0083] (1) Pretreatment of porous materials

[0084] The porous material was immersed in a 60 g / L sodium hydroxide solution and kept in a constant temperature water bath at 55 °C for 18 min. After being removed, it was washed four times with deionized water and then dried at 75 °C for 10 h to obtain the activated porous material.

[0085] The porous material is made of quartz ceramic with a pore size of 5-30μm, an overall wall thickness of 3mm, and a porosity of 25%; the pores are interconnected structures that penetrate the wall material.

[0086] (2) Deposition of silica-based thin film

[0087] The activated porous material was suspended in a silica-based sol, ensuring that the liquid level covered the material. The vacuum was drawn to -0.095 MPa, and low-frequency ultrasound of 40 kHz was applied simultaneously. The material was immersed for 15 minutes, then removed and tilted at 60° to drain for 4 minutes. The surface residual droplets were then blown away under a pressure of 0.12 MPa. The material was then placed at room temperature for 3 hours to remove most of the free water. Subsequently, the temperature was raised to 45°C and held for 2 hours to slowly remove the equilibrium water and reduce volume shrinkage stress. The temperature was then raised to 65°C and held for 2 hours, and then raised to 80°C and held for 2 hours to promote complete hydrolysis and condensation of the sol, forming a dense silica-based thin layer, thus obtaining a silica-based porous material.

[0088] The silica-based sol was prepared by using anhydrous ethanol as a solvent, mixing tetraethyl orthosilicate, anhydrous ethanol and deionized water evenly, adjusting the pH to 3 with 0.4 mol / L hydrochloric acid solution, then adding polyvinyl alcohol, and continuing to stir for 75 min to form a uniform and stable silica-based sol.

[0089] The molar ratio of tetraethyl orthosilicate to anhydrous ethanol is 1:4.4;

[0090] The amount of deionized water added is based on controlling the viscosity of the silica-based sol to 70 mPa·s;

[0091] The amount of polyvinyl alcohol added is 5% of the total mass of the sol.

[0092] (3) Sealing of organosilicon-TEOS hybrid system

[0093] Tetraethyl orthosilicate was added to the organosilicon resin, mixed, and then deionized water was added. The mixture was stirred until homogeneous, and 0.8 mol / L hydrochloric acid solution was added dropwise to adjust the pH to 3. Then, dibutyltin dilaurate was added as a condensation catalyst, and the mixture was stirred at room temperature for 65 min to form an organosilicon-TEOS hybrid system.

[0094] The silica-based porous material was immersed in an organosilicon-TEOS hybrid system, with the liquid level 2 cm above the component. The vacuum was drawn to -0.095 MPa, and low-frequency ultrasound of 40 kHz was applied simultaneously. The immersion was carried out for 50 min. The component was then removed, the surface resin was wiped clean, and the material was dried at room temperature for 2 h. The temperature was then raised to 40 °C and dried for 2 h. Finally, the temperature was raised to 65 °C and cured for 3 h. After cooling, the material was removed and the excess coating on the surface was removed by polishing to obtain a porous material with an airtight coating.

[0095] The silicone resin is composed of a mixture of high molecular weight silicone resin and low molecular weight silicone resin, with a mass ratio of 10:0.55.

[0096] The high molecular weight organosilicon resin has a number average molecular weight of 15000 g / mol, and the low molecular weight organosilicon resin has a number average molecular weight of 2000 g / mol.

[0097] The solid content of the silicone resin is 55%;

[0098] The mass ratio of the organosilicon resin, tetraethyl orthosilicate, deionized water and dibutyltin dilaurate is 100:10:4.3:0.5.

[0099] Comparative Example 1

[0100] Comparative Example 1 uses the method for preparing the hermetic coating of the irregular thin-walled porous material described in Example 2. The difference is that the silica-based thin layer is omitted, and the activated porous material is directly used for sealing the organosilicon-TEOS hybrid system. All other steps are the same.

[0101] Comparative Example 2

[0102] Comparative Example 2 uses the method for preparing the hermetic coating of the irregular thin-walled porous material described in Example 2. The difference is that the sealing step of the organosilicon-TEOS hybrid system is replaced with organosilicon sealing. The addition of tetraethyl orthosilicate, deionized water and dibutyltin dilaurate to the organosilicon resin is omitted. The silica-based porous material is directly immersed in the organosilicon resin. All other steps are the same.

[0103] Comparative Example 3

[0104] Comparative Example 3 uses the method for preparing the airtight coating of the irregular thin-walled porous material described in Example 2. The difference is that Comparative Example 3 only uses high molecular weight organosilicon resin and does not add low molecular weight organosilicon resin. All other steps are the same.

[0105] Experimental Example 1

[0106] The airtightness of the coated porous materials prepared by the methods of Examples 1-3 and Comparative Examples 1-3 was tested. Negative pressure test: The test sample was connected to the airtightness testing fixture for a negative pressure test. The initial pressure was set to -0.096 MPa, and the airtightness test value was recorded after 60 minutes. Pressure holding test: After a pressure test at 0.2 MPa / 5 minutes, the airtightness test value was recorded, and the pressure drop rate was calculated. No air leakage was observed in the product. The test results are shown in Table 1.

[0107] Table 1

[0108]

[0109] Experimental Example 2

[0110] The porous materials prepared by the methods of Examples 1-3 and Comparative Examples 1-3 after coating and airtightness were subjected to 100 temperature change cycles, and the airtightness of the samples after the test was detected by a negative pressure test method. The temperature change cycle test method was as follows: the test sample was placed at room temperature (25±5℃) for 2 hours to ensure that the initial temperature of the sample was uniform. The temperature was then lowered from room temperature to -40℃ at a rate of 5℃ / min and held for 2 hours. Then the temperature was raised from -40℃ to 80℃ at a rate of 5℃ / min and held for 2 hours. Then the temperature was lowered to -40℃ at a rate of 5℃ / min and held for 2 hours. This cooling-heating cycle was repeated 100 times. After the cycle was completed, the sample was allowed to cool naturally to room temperature, and then the airtightness was tested. The test results are shown in Table 2.

[0111] Table 2

[0112]

[0113] Experimental Example 3

[0114] Vibration tests were conducted on the coated, airtight porous materials prepared by the methods of Examples 1-3 and Comparative Examples 1-3. The airtightness of the samples after the tests was also tested using a negative pressure test method. The vibration test method involved mounting the test sample on the test equipment and then performing a sinusoidal frequency sweep cycle. During the frequency sweep, the vibration frequency was changed throughout the entire frequency range, from a minimum frequency of 5 Hz to a maximum frequency of 2000 Hz, and then back to the minimum frequency of 5 Hz. The logarithmic scan rate used for the frequency sweep was 1 oct / min, and the duration was 1 hour. After the test was completed, the airtightness was tested again. The test results are shown in Table 3.

[0115] Table 3

[0116]

[0117] As can be seen from the test results in Table 1-3, the porous materials prepared in Examples 1-3 after coating and airtightness all showed a pressure drop of less than 0.01 MPa after direct negative pressure test, negative pressure test after multiple temperature change cycles, and negative pressure test after vibration test.

[0118] The direct negative pressure test results of Comparative Examples 1-3 were not significantly different from those of Example 2. Although the pressure during high-pressure holding was significantly higher than that of Example 2, it was still less than 5%, indicating good airtightness.

[0119] Comparative Example 1 lacks a silica-based thin layer and relies solely on the organosilicon hybrid layer to bond with the hydroxyl groups on the substrate surface. Without strong Si-O-Si covalent bonds at the interface, gas easily permeates through tiny gaps in the interface during high-pressure holding, resulting in a doubling of the negative pressure rate compared to the Example 1. Due to the weak interfacial bonding, the coating and substrate deform asynchronously during thermal shrinkage. After multiple temperature cycles, the interface peels off, forming gas permeation channels, leading to the most significant drop in negative pressure. During vibration, relative friction occurs between the coating and the substrate, exacerbating interfacial peeling, expanding the permeation channels, and reducing the negative pressure to -0.078 MPa, still exhibiting the worst stability.

[0120] Comparative Example 2 uses a pure organosilicon coating. The organosilicon resin does not have the reinforcing effect of in-situ silica generation, resulting in insufficient coating density and the presence of trace nanoscale permeation channels. Under high pressure, the gas permeation increases, and the descent rate further increases. Without the rigid support of in-situ silica, it is prone to softening at high temperature (80℃) and brittleness at low temperature (-40℃). After cycling, the coating develops micro-cracks, the gas permeation increases, and the negative pressure drops to -0.081MPa. The pure organosilicon coating lacks toughness and is prone to fatigue cracks under high-frequency vibration, resulting in increased gas permeation and a drop in negative pressure to -0.085MPa.

[0121] Comparative Example 3, with its coating structure filled by a single high molecular weight resin, exhibits unevenness. The high molecular weight resin cannot completely fill the micropores and pore edges, resulting in localized sealing defects. Under high pressure, these defects become gas permeation channels, exhibiting the highest rate of reduction and the worst initial sealing reliability. During thermal contraction, the internal stress distribution is uneven, leading to localized coating bulging or microcracks, which compromises the seal integrity, causing the negative pressure value to drop to -0.078 MPa. Although there are no interface short plates, the initial defects caused by micropore sealing are further amplified during vibration. However, due to the absence of interface peeling issues, the pressure drop is slightly better than that of Comparative Examples 1-2.

[0122] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an airtight coating for an irregularly shaped thin-walled porous material, characterized in that, The method includes the following steps: pretreatment of porous materials, deposition of a silica-based thin layer, and sealing with an organosilicon-TEOS hybrid system; The method for depositing a silica-based thin layer is as follows: the activated porous material is suspended in a silica-based sol, ensuring that the liquid surface covers the material. Under vacuum conditions, low-frequency ultrasound is applied simultaneously, and the material is immersed for 15-20 minutes. The component is then removed, tilted to drain for 4-6 minutes, and the surface residual droplets are blown away. The material is then placed at room temperature for 2-3 hours, followed by heating to 35-45℃ and holding for 2-3 hours, then heating to 55-65℃ and holding for 2-3 hours, and finally heating to 70-80℃ and holding for 2-3 hours to form a dense silica-based thin layer, thus obtaining a silica-based porous material. The method for sealing the organosilicon-TEOS hybrid system is as follows: add tetraethyl orthosilicate to organosilicon resin, mix, then add deionized water, stir evenly, add hydrochloric acid solution to adjust the pH to 2-3, then add dibutyltin dilaurate as a condensation catalyst, stir at room temperature for 55-65 minutes to form the organosilicon-TEOS hybrid system. The silica-based porous material is immersed in an organosilicon-TEOS hybrid system, with the liquid level covering the component. Under vacuum conditions, low-frequency ultrasound is applied simultaneously, and the immersion time is 50-70 minutes. The component is then removed, the surface resin is wiped clean, and the material is dried at room temperature for 2-3 hours. The temperature is then raised to 30-40℃ and dried for another 2-3 hours. Finally, the temperature is raised to 55-65℃ and cured for 3-4 hours. After cooling and removal, the excess coating on the surface is removed by polishing to obtain a porous material with an airtight coating. The silicone resin is composed of a mixture of high molecular weight silicone resin and low molecular weight silicone resin, with a mass ratio of 10:0.45-0.

55. The high molecular weight organosilicon resin has a number average molecular weight of 10,000-15,000 g / mol, and the low molecular weight organosilicon resin has a number average molecular weight of 1,000-2,000 g / mol. The solid content of the organosilicon resin is 45-55%.

2. The method for preparing an airtight coating for a non-circular thin-walled porous material according to claim 1, characterized in that, In the step of depositing a silica-based thin layer, the silica-based sol is prepared by mixing tetraethyl orthosilicate, anhydrous ethanol and deionized water evenly with anhydrous ethanol as solvent, adjusting the pH to 2-3 with hydrochloric acid solution, then adding polyvinyl alcohol and stirring for 65-75 minutes to form a silica-based sol.

3. The method for preparing an airtight coating for a non-circular thin-walled porous material according to claim 2, characterized in that, In the preparation steps of the silica-based sol, The molar ratio of tetraethyl orthosilicate to anhydrous ethanol is 1:3.6-4.4; The amount of deionized water added is based on controlling the viscosity of the silica-based sol to 50-70 mPa·s; The amount of polyvinyl alcohol added is 3%-5% of the total mass of the sol.

4. The method for preparing an airtight coating for a non-circular thin-walled porous material according to claim 1, characterized in that, The vacuum gauge pressure is -0.095 to -0.085 MPa, the low-frequency ultrasound frequency is 20-40 kHz, and the tilt angle of the drain is 30°-60°.

5. The method for preparing an airtight coating for a non-circular thin-walled porous material according to claim 1, characterized in that, The method for pretreating the porous material is as follows: immerse the porous material in a sodium hydroxide solution and keep it in a constant temperature water bath at 45-55℃ for 18-22 minutes. After taking it out, wash it with deionized water 3-4 times, and then dry it at 65-75℃ for 10-14 hours to obtain the activated porous material.

6. The method for preparing an airtight coating for a non-circular thin-walled porous material according to claim 5, characterized in that, The porous material has a pore size of 5-30 μm, an overall wall thickness of 2.5-3 mm, and a porosity of 20-25%; wherein the pores are interconnected structures that penetrate the wall material. The porous material is made of quartz ceramic; The concentration of the sodium hydroxide solution is 40-60 g / L.

7. The method for preparing an airtight coating for a non-circular thin-walled porous material according to claim 1, characterized in that, In the sealing step of the organosilicon-TEOS hybrid system, the mass ratio of the organosilicon resin, tetraethyl orthosilicate, deionized water and dibutyltin dilaurate is 100:8-10:3.7-4.3:0.3-0.

5.

8. The method for preparing an airtight coating for a non-circular thin-walled porous material according to claim 1, characterized in that, In the sealing step of the organosilicon-TEOS hybrid system, the gauge pressure of the vacuum is -0.095 to -0.085 MPa, and the frequency of the low-frequency ultrasound is 20-40 kHz.

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